Method of sealing a panel to an aircraft structure

ABSTRACT

The invention relates to a method of providing a seal between an aircraft structure ( 14 ) and a removable panel ( 26 ) mountable on the structure to close an opening ( 12 ) therein. According to the invention, the method comprises applying a sealant compound ( 28 ) for example a polysulphide rubber compound, to one of the structure and the panel, forming a rebate ( 46 ) in the sealant compound, and providing a sealant tape ( 48 ) to fit within the rebate. Subsequently, the panel is fastened to the structure with the seal ( 50 ) comprising the sealant compound and the sealant tape being sandwiched between the structure and the panel and encircling the opening.

This is a divisional National Application No. 09/585,558 filed Jun. 2,2000 now U.S. Pat. No. 6,461,458 which was a continuation ofInternational Application No. PCT/GB00/01356 filed Apr. 11, 2000 whichdesignated the U.S.

This invention concerns a method and apparatus for providing a sealbetween an aircraft structure and a removable panel, and an aircraft oraircraft section having such a seal.

In particular, this invention concerns a method of providing awatertight seal between an aircraft structure having an opening thereinand a removable panel mountable on the structure to close the opening.The method has particular application in the sealing of interchangeablepanels over aircraft chambers containing, for example, fuses and/orother sensitive equipment requiring access for maintenance and servicepurposes. A particular application is in the sealing of radar bay accesspanels on aircraft.

Conventionally, it is known to seal radar bay access panels to thesurrounding aircraft structure using a polysulphide rubber compound as asealant between the panel and a portion of the aircraft structuredefining an access opening to the radar bay, the panel being attached tothe structure by means of fasteners extending through the sealantcompound, and grommets.

However, test procedures have established that inadequate sealing isobtained by these means and that water ingress occurs in the spacesbetween the fasteners. It is thought that this is due to the fastenerscompressing the panel against the sealant in their immediate locationbut having an irregular pitch so that the panel is not properly heldagainst the sealant compound between the fasteners when there is arelatively large spacing between them. Consequently, whilst sufficientsealing may be provided for panels covering for example standard storagespaces or relatively insensitive equipment, such sealing does not meetthe requirements for electrical and other sensitive equipment.

Commercial sealant tape is also available but has not hitherto beenemployed for sealing panels to aircraft structures because the tape doesnot possess the load bearing characteristics required for suchconditions.

According to the present invention, there is provided a method ofproviding a seal between an aircraft structure and a removable panelmountable on the structure to close an opening therein, comprising:

-   -   applying a sealant compound to either the structure or the        panel,    -   forming a rebate in the sealant compound,    -   providing a sealant tape to fit within the rebate, and    -   fastening the panel to the structure with the seal comprising        the sealant compound and the sealant tape being sandwiched        between the structure and the panel and encircling the opening.

The combination of the sealant compound and the sealant tape has beenfound to provide a seal which is far superior to the seal obtained bythe use of either alone.

Preferably, the sealant compound is applied to the aircraft structure.

In the preferred form of the method described below, the sealantcompound is then set or cured and the rebate is formed in the sealantcompound at the same time, then subsequently the tape is applied to therebate.

The sealant compound may be a polysulphide rubber compound.

According to another aspect of the invention, there is provided anaircraft or aircraft section having a structure containing an openingtherein, a removable panel for closing the opening, and a seal providedbetween the panel and the structure, the seal comprising:

-   -   a sealant compound surrounding the opening and having a rebate        formed therein, and    -   a sealant tape provided in the rebate.

The invention also provides apparatus for providing a seal between anaircraft structure and a removable panel mountable on the structure toclose an opening therein, comprising:

-   -   means for applying a sealant compound to one of the structure        and the panel,    -   means for forming a rebate in the sealant compound,    -   means for providing a sealant tape to fit within the rebate, and    -   means for fastening the panel to the structure with the seal        comprising the sealant compound and the sealant tape being        sandwiched between the structure and the panel and encircling        the opening.

In addition, the invention provides a tool for use in the method,comprising a setting frame for impressing a liquid sealant compound asemployed in the method and means for curing the liquid sealant compound,the frame having a substantially continuous forming surface, and asubstantially continuous rib upstanding from the forming surface alongthe full extent thereof.

The invention is described further, by way of example, with reference tothe accompanying drawings in which:

FIG. 1 shows a fragmentary section through an aircraft structure havingan opening therein to be closed by a removable panel; and apertures setabout the opening;

FIG. 2 is a fragmentary section corresponding to FIG. 1 and showing ablanking pin applied to a respective aperture;

FIG. 3 is a fragmentary section corresponding to FIG. 1 and showinguncured sealant applied to the aircraft structure about the opening;

FIG. 4 is a fragmentary section corresponding to FIG. 1 and showing asetting tool being applied to the sealant compound;

FIG. 5 is fragmentary section corresponding to FIG. 1 and showing thesealant compound in the course of being trimmed;

FIG. 6 is a fragmentary section corresponding to FIG. 1 and showing thesealant compound ready for use in a seal;

FIG. 7 is a fragmentary section corresponding to FIG. 1 and showing theremovable panel about to be fitted to the aircraft structure.

Referring initially to FIG. 1, this shows an aircraft section 10 havingtherein an opening 12 providing access to a radar bay (not shown) of theaircraft. The aircraft section 10 comprises a structure 14, having asub-frame 16 defining the opening 12 and a skin 18 set back from theopening 12 so that a surface 20 of the sub-frame 16 is exposed inside anedge 22 of the skin 18. Apertures 24, one of which is shown in FIG. 1,are provided in the exposed area 20 of the sub-frame 16 for receivingfasteners for attaching a panel 26 (shown in FIG. 7) to the structure14.

In order to ensure a watertight seal in use between the structure 14 andthe panel 26, sealing means are provided between them and the method ofproducing these sealing means is illustrated in FIGS. 2 to 7.

In the first step of the sealing method illustrated in FIG. 2, arespective blanking pin 27 is fitted in the illustrated opening 24, theblanking pin 27 having been treated with release agent before use.

In the second step of the sealing method illustrated in FIG. 3, a liquidsealant compound 28 is applied over the full surface 20 of the sub-frame16 encircling the opening 12 inside the edge 22 of the skin 18. Theliquid sealant compound 28 flows over this surface 20 in order to coverit fully, but the blanking pins 27 prevent the liquid sealant compoundfrom entering the apertures 24. In the present instance, a polysulphiderubber compound is used for the sealant compound.

In the next step of the method, illustrated in FIG. 4, a setting tool 30is applied to the surface of the liquid sealant compound 28 in orderboth to cure the sealant compound and to form the compound into asuitably shape for sealing purposes. The setting tool 30 is also treatedwith a release agent before use, and either an external heat sauce orheating means within the setting tool 30 may be used to acceleratecuring.

As shown in FIG. 4, the setting tool comprises an open metal frame 34having a profile corresponding to that portion 20 of the structure 14surrounding the opening 12 and having therein a plurality of apertures36 corresponding to the apertures 24 in the structure 14 and arranged tofit over the blanking pins 27. An outer surface 38 of the setting tool30 is of marginally smaller dimensions than the spacing between opposedportions of the edge 22 of the skin 18 for reasons set out below. Inaddition, the setting tool 30 has an upstanding rib 40 extending all theway round the frame 34, also for reasons set out below.

When the setting tool 30 is applied to the liquid sealant compound 28,those portions of the compound which are heated are impressed and curedand become set. The remaining portions of the compound in the region ofthe opposed surfaces 22, 38 of the skin 18 and tool 34 and adjacent theopening 12 are subsequently trimmed away as illustrated in FIG. 5.

After this, the setting tool 34 and blanking pins 27 are removed toleave a sealing element 41, as illustrated in FIG. 6, which has a land42 covering the surface 20 of the sub-frame 16 surrounding the opening12, and an upstanding rim 44 flanking the edge 22 of the skin 18. Acontinuous rebate 46 is formed in the sealing element 41 by the rib 40of the setting tool 30, and extends all the way around the opening 12.Apertures 47 are also provided in register with the apertures 24,through the use of the blanking pins 27.

Next, a sealant tape 48 having an integral adhesive surface is fitted tothe rebate 46 along the full extent of its length. The sealant tape 48consequently encircles the opening 12 completely, and the sealingelement 41 and sealant tape 48 together provide a seal 50 around theopening 12. It is to be noted that the upper surface of the sealant tape48 is raised a little relative to the adjacent surface of the sealingelement 41.

Next, the panel 26 is applied to the aircraft structure 14 as shown. Theremovable panel 26 is sized to be an interference fit within theupstanding rim 44 of the sealing element 41, and is formed withapertures 52 corresponding to the apertures 24 in the sub-frame 16designed to receive fasteners (not shown). As the panel 26 is loweredonto the structure 14, it first comes into contact with the raisedsurface of the sealant tape 48 and then compresses the sealant tape 48and also the sealing element 41. The fastening means applied between thepanel 26 and the sub-frame 16 maintain this compressed state of thesealant tape 48 and the sealing element 41 and ensure that a watertightseal 50 is provided between the panel 26 and the aircraft structure 14.

Experimental tests have demonstrated that a good watertight seal andadequate load bearing capabilities in normal aircraft conditions can beobtained by the combination of the sealing element 41 and the sealanttape 48, whereas neither one on its own is sufficient to the task.

A number of modifications are possible in the described method. Forexample, the sealant tape can be applied initially to the panel 26rather than to the sealing element 41, so long as it is aligned with therebate 46 in the sealing element 41. The effect will be the same oncethe panel 26 has been fitted to the structure 14.

Another possibility is for the sealant compound 28 to be applied to thepanel 26 in the first instance, and for the setting tool 30 to cure thecompound on the panel 26. A rebate 46 is then conveniently provided inthe same manner as before, and sealant tape 48 may be applied eitherdirectly to the rebate 46 of the cured sealing element 41 or indirectlyduring the assembly of the panel 26 to the aircraft structure 14.

In the described embodiment of the method, the sealant compound 28 maybe set or cured by heating but alternative setting means, for examplechemical, may also be employed.

The sealing compound in the method described above is a standardpolysulphide rubber compound, but other sealant compounds may also beemployed.

1. An aircraft or aircraft section having a structure containing anopening therein, a removable panel for closing the opening, and a sealprovided between the panel and the structure, the seal comprising: asealant compound, surrounding the opening and having a rebate formedtherein, and a sealant tape provided in the rebate, each of the sealantcompound and the sealant tape being in contact with the panel forproviding the seal between the panel and the structure.
 2. An aircraftor aircraft section according to claim 1 wherein the structure comprisesa sub-frame defining the opening and a skin set back from the opening,and wherein the sealant compound forms a land on the sub-frame about theopening and an upstanding rim flanking an edge of the skin.
 3. Anaircraft or aircraft section according to claim 2 wherein the panel isreceived within the rim of the sealant compound to be contiguous withthe skin.
 4. An aircraft or aircraft section according to any of claims1 further comprising fastener openings in the sealant compound andfastening means for fastening the panel to the structure, the fasteningmeans extending through the fastener openings.
 5. An aircraft oraircraft section according to claim 2 further comprising fasteneropenings in the sealant compound and fastening means for fastening thepanel to the structure, the fastening means extending through thefastener openings.
 6. An aircraft or aircraft section according to claim3 further comprising fastener openings in the sealant compound andfastening means for fastening the panel to the structure, the fasteningmeans extending through the fastener openings.
 7. An aircraft oraircraft section according to claim 1 wherein the sealant compound is apolysulphide rubber compound.
 8. An aircraft section comprising: anaircraft structure having an opening therein, the structure including aninner element defining the opening and an outer element on the innerelement and set back from the opening such that a surface of the innerelement is exposed inside an edge of the outer element; a removablepanel mountable on the structure to close the opening; and a sealassembly for providing a seal between the aircraft structure and theremovable panel, the seal assembly comprising: a sealant compoundincluding a land engaging the surface of the inner element in sealingrelation and an upstanding rim engaging the edge of the outer element insealing relation, the land including a rebate formed therein and anaperture aligned with the opening; and a sealant tape being distinctfrom the sealant compound and formed separately from the sealantcompound and being provided in the rebate of the sealant compound, andeach of the sealant compound and the sealant tape engaging the removablepanel in sealing relation such that the sealant compound and the sealanttape together provide a seal around the opening of the structure.